International projects TIMSS, PISA and similar deal with testing pupils' knowledge, among others in mathematics. The public notices their results especially in terms of ranking countries according to their success in these tests. It turns out, however, that the dependence of success in tests on the county, from which pupils come, cannot be proved. Rather, there is a dependence on competence of these pupils' teachers. This competence, however, is difficult to test - both in the Czech Republic and...